An optical fiber having a structure that an optical bare fiber composed of a silica-based glass such as pure glass is coated with a resin layer is usually formed by melt-drawing a silica-based glass preform by means of a drawing apparatus to form an optical bare fiber and subsequently applying a curable resin composition on the outer circumference of the optical bare fiber by means of a coating die or the like, followed by curing. Moreover, the adhesion between the optical bare fiber and the coating layer has been improved by incorporating a silane coupling agent into the above curable resin composition.
In the case where the coating layer is formed of a material containing a silane coupling agent, strength deterioration is accelerated. In order to solve this problem, Patent Document 1 discloses a method of forming the coating layer on an optical bare fiber with the material containing the silane coupling agent, subsequently heating the layer under a high-humidity atmosphere, and then subjecting it to a drying treatment.
Furthermore, after the coating layer is formed of the curable resin composition containing the silane coupling agent on the outer circumference of the optical bare fiber, for example, the optical fiber is taken up on a bobbin.
Patent Document 1: JP-A-63-11550